Semiconductor device

ABSTRACT

Each lead frame for a power chip has one side main surface on which a power chip is mounted and a suspension lead part provided projectingly from a region reserved for forming mold resin in addition to a lead terminal. Thus, the lead frame can be supported by the plurality of suspension lead parts in a molding step. A metal block is provided on the other main surface of the lead frame to face the power chip. Consequently, a semiconductor device with good heat radiation properties and good insulation breakdown voltages can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a semiconductor device,and more particularly to a structure of a power semiconductor deviceused for power control,

2. Description of the Background Art

FIG. 15 is a sectional view schematically illustrating a structure of apower semiconductor device according to the background art. As shown inFIG. 15, the power semiconductor device according to the background artcomprises a power chip 1 having a power element, a lead frame 20 made ofa metal thin plate, a metal block 5 functioning as a heat sink forradiation and a mold resin 6.

The lead frame 20 has a die pad part 3 and an inner lead part 4. Thepower chip 1 is jointed to the die pad part 3 with solder 9 as a binder.An electrode (not shown) formed on the power chip 1 is connected to theinner lead part 4 of the lead frame 20 by an aluminum wire 8. The metalblock 5 has a projection almost at its center and is arranged such thatthe projection faces the power chip 1 leaving a predetermined spacingwith respect to a surface of the lead frame 20 opposite to the powerchip 1. The mold resin 6 exposes a surface of the metal block 5 oppositeto the lead frame 20 while sealing the power chip 1, the lead frame 20and the metal block 5.

Attached to the exposed part of the metal block 5 is an external heatradiator 11. Part of the mold resin 6 present between the projection ofthe metal block 5 and the lead frame 20 is called a resin insulationlayer 27.

In the power semiconductor device according to the background art, heatgenerated in the power chip 1 is emitted to the outside from theexternal heat radiator 11 through the lead frame 20, the resininsulation layer 27 and the metal block 5. The metal block 5 and theexternal heat radiator 11 made of aluminum or copper and have thermalconductivities of approximately 230 W/mK and approximately 390 W/mK,respectively. The lead frame 20, which is also made of metal such ascopper, has a thermal conductivity of substantially the same degree asthe metal block 5 and the external radiator 11. The resin forming theresin insulation layer 27 has a thermal conductivity of 1-3 W/mK. Thus,the resin insulation layer 27 has the thermal conductivity ofsubstantially one hundredth that of any other material. This is a mainfactor that hinders thermal conduction.

Heat radiation properties of a semiconductor device are determined bythe thickness and thermal conductivity of a material through which heatis conducted, an area of the material through which heat is conducted,and the like. The power semiconductor device according to the backgroundart can achieve improved heat radiation properties by thinning the resininsulation layer 27 to thereby reduce part that has a low thermalconductivity through which heat is conducted. However, the resininsulation layer 27 needs an insulation breakdown voltage of severalthousands of volts. This imposes limitations on its thickness to fallinto the neighborhood of 0.5 mm, and improvements in the heat radiationproperties are thus limited.

The thermal conductivity of the resin insulation layer 27 could beincreased to as high as approximately 5 W/mK by using ceramic powderhaving a high thermal conductivity such as aluminum nitride powder orsilicon nitride powder as a filler for the resin forming the resininsulation layer 27 to increase a filling factor. However, the resininsulation layer 27 is part of the mold resin 6, which causes the resinfilled with ceramic powder to be used even for elements other than theresin insulation layer 27, i.e., elements that do not require highthermal conductivities. This results in a wasted use of expensive resin.In consequence, material costs of a semiconductor device are increased.

Heat generated in the power chip 1 is first conducted through the leadframe 20, and next, through the resin insulation layer 27. It isgenerally impossible to make the lead frame 20 thick in terms ofprocessing unlike the metal block 5 or the like. Thus, the lead frame 20has a thermal diffusion effect inferior to that of the metal block 5 orthe like. This makes it difficult to fully extend an area of the resininsulation layer 27 through which heat is conducted, which has been afactor that imposes limitations on improvements in heat radiationproperties.

SUMMARY OF THE INVENTION

It is an object of the present invention is to provide a semiconductordevice with good heat radiation properties and good insulation breakdownvoltages.

According to the present invention, the semiconductor device includesfirst a second semiconductor chips, first and second lead frames, ametal block, and resin. The first and second lead frames have one sidemain surfaces on which the first and second semiconductor chips aremounted, respectively. The metal block is provided on the other mainsurface of the first lead frame. The resin is formed to cover the firstand second semiconductor chips, the first and second lead frames and themetal block. The first lead frame has a plurality of suspension leadparts projecting from the resin.

The present invention radiates well heat generated in the firstsemiconductor chip by means of heat radiation through the metal blockprovided on the other main surface of the first lead frame. At thistime, the metal block, which is covered with resin, can maintaininsulation relationship with the outside.

Further, the first lead frame, having the plurality of suspension leadparts, is brought into a state of a beam supported at two or morepositions at least in the resin molding step, according to which itsstiffness can be improved. This allows the resin covering the metalframe to be formed uniformly in thickness. As a result improved heatradiation properties can be obtained while securing insulationproperties.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically illustrating a structure of asemiconductor device according to the basic principle of the presentinvention;

FIG. 2 is an explanatory view illustrating the way heat is conducted ina semiconductor device according to the background art;

FIG. 3 is an explanatory view illustrating the way heat is conducted inthe semiconductor device according to the basic principle shown in FIG.1;

FIG. 4 is a sectional view illustrating a sectional structure of a powersemiconductor device including a plurality of types of chips;

FIG. 5 is an explanatory plan view briefly illustrating a power chip tobe mounted on a lead frame;

FIG. 6 is a plan view schematically illustrating a planar structure of apower semiconductor device according to a first preferred embodiment ofthe present invention before resin sealing;

FIG. 7 is a plan view schematically illustrating a planar structure ofthe power semiconductor device according to the first preferredembodiment after the resin sealing;

FIG. 8 is a sectional view schematically illustrating a sectionalstructure of the power semiconductor device according to the firstpreferred embodiment after the resin sealing;

FIG. 9 is a sectional view illustrating a side structure of the powersemiconductor device according to the first preferred embodiment afterthe resin sealing;

FIG. 10 is a plan view schematically illustrating a planar structure ofa power semiconductor device according to a second preferred embodimentof the invention before resin sealing;

FIG. 11 is a sectional view schematically illustrating a sectionalstructure of the power semiconductor device according to the secondpreferred embodiment after the resin sealing;

FIG. 12 is an explanatory view schematically illustrating the state ofpartial metal blocks adjacent to each other;

FIG. 13 is a plan view schematically illustrating a peripheral structureof a suspension lead part of a power semiconductor device according to athird preferred embodiment of the invention;

FIG. 14 is a plan view schematically illustrating a peripheral structureof a suspension lead part of a power semiconductor device according to afourth preferred embodiment of the invention; and

FIG. 15 is a sectional view schematically illustrating a structure ofthe power semiconductor device according to the background art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Basic Principle>

(Power Semiconductor Device Including a Metal Block)

FIG. 1 is a sectional view schematically illustrating a structure of asemiconductor device according to a basic principle of the presentinvention. As shown in FIG. 1, the semiconductor device according to thebasic principle includes the power chip 1, lead frames 20 a, 20 b, themetal block 5 and the mold resin 6.

The lead frames 20 a and 20 b are made of metal having a good thermalconductivity such as a thin plate of a copper alloy. The lead frame 20 ahas the die pad part 3 and the inner lead part 4, and the lead frame 20b has the inner lead part 4. The power chip 1 has electrodes (not shown)provided on its both surfaces, and is mounted on the die pad part 3 ofthe lead frame 20 a and jointed thereto with the solder 9 such that oneof the electrodes on one of its surfaces is in contact with the leadframe 20 a. The other of the electrodes on the other surface of thepower chip 1 is connected to the inner lead part 4 of the lead frame 20b by the aluminum wire 8. The lead frames 20 a and 20 b are separatedfrom each other, and the electrodes formed on the both surfaces of thepower chip 1 are insulated from each other.

The metal block 5, made of aluminum or copper, for example, is jointedto the lead frame 20 a with a jointing material 10 on one surfaceopposite to the power chip 1. More specifically, the metal block 5 has ajunction surface 50 and a non-junction surface 51 on its one side mainsurface and is arranged such that the junction surface 50 and thenon-junction surface 51 face the lead frames 20 a and 20 b. The junctionsurface 50 is formed projectingly toward the power chip 1 further thanthe non-junction surface 51 and is jointed to the lead frame 20 a withthe jointing material 10 so as to face the power chip 1.

In other words, the metal block 5 has a projection on one of itssurfaces, and the projection is jointed to the lead frame 20 a so as toface the power chip 1. The other surface of the metal block 5 oppositeto the lead frame 20 a is larger than a surface of the power chip 1jointed to the lead frame 20 a. The non-junction surface 51 and the leadframe 20 b form an insulation space 60 therebetween.

The mold resin 6, made of epoxy resin, for example, provides aninsulation layer 7 for the metal block 5 on the surface opposite to thelead frames 20 a and 20 b while covering and sealing the power chip 1,the lead frames 20 a, 20 b and the metal block 5. The external heatradiator 11 is attached to the insulation layer 7 on a surface oppositeto the metal block 5.

In the semiconductor device of the basic principle having theabove-described structure, heat generated in the power chip 1 isconducted through the solder 9, the lead frames 20 a, 20 b, the jointingmaterial 10, the metal block 5 and the insulation layer 7, and isemitted to the outside from the external heat radiator 11. The jointingmaterial 10 is not required to ensure electric insulation between thelead frame 20 a and the metal block 5. Thus, any material can beemployed without considering its insulation breakdown voltage. Morespecifically, when another semiconductor device is attached to theexternal heat radiator 11, the insulation layer 7 maintains insulationbetween the semicondutor devices. Thus, it is not necessary to considerthe insulation breakdown voltage of the jointing material 10. Therefore,the joining material 10 may be made of a material such as solder thathas a thermal conductivity better than that of the insulation layer 7.As a result, heat generated in the power chip 1 is conducted well fromthe lead frame 20 a to the metal block 5.

Moreover, even in the case in which a resin adhesive is employed as thejointing material 10, the jointing material 10 can be made thinner thanthe resin insulation layer 27 in the aforementioned background art. Morespecifically, the thickness of the jointing material 10 can be set at10-40 μm and can be reduced to substantially one tenth that of theconventional resin insulation layer 27. Alternatively, an adhesive mixedwith, for example, metal powder as a filler, i.e., a binder having ahigh thermal conductivity may be used. In consequence, the jointmaterial 10 made of a resin adhesive can be improved in the thermalconductivity 5 to 10 times (5-20 W/mK) that of the conventional resininsulation layer 27. That is, even when a resin adhesive is used for thejointing material 10, heat generated in the power chip 1 can beconducted well to the metal block 5.

Next, heat conducting through the insulation layer 7 which is a mainfactor that hinders heat conduction will be described in detail. FIGS. 2and 3 illustrate the way heat generated in the power chip 1 isconducted. FIG. 2 shows the way heat is conducted in the powersemiconductor device according to the above described background art,and FIG. 3 shows the way heat is conducted in the semiconductor deviceaccording to the basic principle. As indicated by a thermal diffusiondirection 30 in FIG. 2, heat generated in the power chip 1 is diffusedin a slightly horizontal direction at the lead frame 20 in thebackground art, however, diffusion is not carried out sufficiently dueto the thinness of the lead frame 20. Thus, an area 32 of the resininsulation layer 27 which is a main factor that hinders heat conductionin the background art through which heat is conducted is almost the sameas the area of the power chip 1. On the other hand, as indicated by athermal diffusion direction 31 in FIG. 3, heat generated in the powerchip 1 is diffused in a slightly horizontal direction at the lead frame20 a and is further diffused at the metal block 5 having a sufficientthickness in the basic principle. Therefore, an area 33 of theinsulation layer 7 through which heat is conducted is sufficientlylarger than the area of the power chip 1. In short, a main factor thathinders heat conduction in the basic principle is smaller than that inthe background art.

As has been described, the semiconductor device according to the basicprinciple provides improved heat radiation properties.

Further, since the metal block 5 and the lead frame 20 b form theinsulation space 60 therebetween, the metal block 5 may be increased insize as nearly large as the outside dimension of the semiconductordevice while the electrodes on the both surfaces of the power chip 1 areinsulated from each other. As a result improved heat radiationproperties can be obtained.

Furthermore, the lead frame 20 a and the metal block 5 are jointed justbefore the step of forming the mold resin 6 in the basic principle.Thus, manufacturing can be performed up to the wiring of the aluminumwire 8 by the same process and apparatus as conventional ones. Thispermits a reduction of new capital investments and the like.

(Power Semiconductor Device Including a Plurality of Types of Chips)

A general power semiconductor device is equipped with: a power chip forswitching a large current having an element such as an insulated gatebipolar transistor (hereinafter referred to as “IGBT”) or a fly wheeldiode (hereinafter referred to as “FWD”); and an integrated circuit chipfor controlling the power chip such as a low voltage integrated circuit(hereinafter referred to as “LVIC”) or a high voltage integrated circuit(hereinafter referred to as “HVIC”).

In other words, the power chip and the integrated circuit chip on whichthe aforementioned metal block is to be formed are mounted on leadframes different from each other, and predetermined parts such as a chipand a frame are electrically connected by using a wire bonding techniqueor equivalent. Thereafter, a resin molding step is carried out, therebyforming the power semiconductor device including a plurality of types ofsemiconductor chips.

FIG. 4 is a sectional view illustrating a structure of such powersemiconductor device. As shown in FIG. 4, a power chip 41 and anintegrated circuit chip 42 are jointed to one side main surfaces of leadframes 2 a and 2 c, respectively, with a jointing material 46 by using adie bonding technique. Next, the power chip 41 is electrically connectedto part of predetermined inner leads of the lead frames 2 a and 2 c byan aluminum wire 44. Further, the integaed circuit chip 42 and apredetermined inner lead of the lead frame 2 c are electricallyconnected by a gold wire 43. The reason for employing the aluminum wire44 is that the power chip handles a large current.

On the other hand, a metal block 47 having a projection in a regioncorresponding to the power chip 41 is jointed to the other main surfaceof the lead frame 2 a with a jointing material 48.

Further, a mold resin 45 such as epoxy resin is used to perform transfermolding, thereby covering and sealing the power chip 41, the integratedcircuit chip 42, the lead frames 2 a, 2 c and the metal block 47.

The lead frames 2 a and 2 c are bent at their ends such that they areused as lead terminals 2 b and 2 d.

In such power semiconductor device including a plurality of types ofsemiconductor chips, the power chip 41 is formed on the side of the leadterminal 2 b and the integrated circuit chip 42 on the side of the leadterminal 2 d. Therefore, the lead frame 2 a on which the power chip 41is mounted is in a cantilever state that is supported only by the sideof the lead frame 2 b in the molding step.

In the molding step, viscous force resulting from resin flow is added tothe lead frame 2 a on which the power chip 41 is mounted. The lead frame2 a is in the cantilever state as described above, it has a lowstiffness and is easily deformed or displaced. More specifically, therearises a problem in that the lead frame 2 a is easily inclined in theflowing direction of the mold resin 45. In consequence, an inclinationof the lead frame 2 a results in non-uniformity of the mold thickness ofthe mold resin 45 under the power chip 41.

Therefore, a thin part and a thick part are generated in the mold resin45. There is concern that the thin part 45 a of the mold resin 45 underthe metal block 47 may have faulty insulation. Therefore, the mold resinneeds to be sufficiently thick for carrying out the molding step. Inthis case, however, a problem arises in that the mold thickness becomesthicker than necessary at the thick part and the thermal resistance isthus increased, resulting in hindrance of heat radiation.

FIG. 5 is an explanatory plan view briefly illustrating the power chip41 to be mounted on the lead frame 2 a. Generally, as shown in FIG. 5, aplurality of power chips 41 are formed on a plurality of (partial) leadframes 2 a provided adjacently to one another.

In the case that the lead frame 2 a on which the power chip 41 ismounted shown in FIG. 5 has a region 2 r extending diagonally withrespect to an injecting direction D1 of the mold resin, the lead frame 2a may be deformed and vertically bent to the flowing direction of themold resin, causing concern that contact failure might occur betweenadjacent lead frames 2 a and 2 a. To prevent this, the lead frames 2 aneed to be increased in width to improve their stiffness. However, anincrease in the width of the lead frames 2 a reduces an insulationdistance d2 between adjacent lead frames 2 a and 2 a, causing aproblematic deterioration in insulation properties. In order to maintaininsulation properties, a pitch between adjacent lead frames 2 a and 2 aneeds to be widened. This causes a problem in that a device has to beincreased in size.

Further, another problem arises in that an increase in an area of themetal block 47 that is in contact with the flow of the mold resin and anincrease in the accompanying viscous force cause the above problem to bemore significant.

<First Preferred Embodiment>

FIG. 6 is a plan view schematically illustrating a planar structure of apower semiconductor device according to the first preferred embodimentof the invention before resin sealing. FIG. 7 is a plan viewschematically illustrating a planar structure of the power semiconductordevice according to the first preferred embodiment after the resinsealing. FIG. 6 shows a region 55 reserved for forming mold resin bydotted lines.

In the power semiconductor device, the power chip 41 including the powerchip 1 for switching a large current such as IGBT or FWD and theintegrated circuit chip 42 for controlling the power chip 41 such asLVIC or HVIC are mounted on the lead frames 2 a and 2 c, respectively.

As shown in FIG. 6, each (partial) lead frame 2 a for the power chip hasa suspension lead part 2 e to be used as a support in the resin sealingprovided projectingly from the region 55 in addition to the leadterminal 2 b. The lead frame 2 a can thus be supported by a plurality ofsuspension lead parts 2 b and 2 e in the molding (the resin sealingstep).

FIG. 8 is a sectional view schematically illustrating a sectionalstructure of the power semiconductor device according to the firstembodiment after the resin sealing. FIG. 9 is a sectional viewillustrating a side structure of the power semiconductor deviceaccording to the first embodiment after the resin sealing. FIG. 8corresponds to a section taken along the line A—A of FIG. 7, and FIG. 9corresponds to a side surface viewed from the lead terminal 2 d side ofFIG. 7.

Referring to FIGS. 6 to 9, a method of manufacturing the powersemiconductor device according to the first embodiment will bedescribed.

The power chip 41 and the integrated circuit chip 42 are mounted on oneside main surfaces of the lead frames 2 a and 2 c, respectively, withthe jointing material 46 using the die bonding technique.

Next, the power chip 41 and part of predetermined inner leads of thelead frame 2 a are electrically connected by the aluminum wire 44 usingthe wire bonding technique. The integrated circuit chip 42 andpredetermined inner leads of the lead frame 2 c are also electricallyconnected by a gold wire 43.

The metal block 47 is placed on the other main surface of the lead frame2 a opposite to its one side main surface so as to face the power chip41 and is jointed thereto with the jointing material 48. The metal block47 can thus be provided on the other main surface of the lead frame 2 a.

Thereafter, transfer molding is performed using epoxy resin, forexample, thereby covering and sealing the power chip 41, the integratedcircuit chip 42 and the metal block 47 with the mold resin 45.

Lastly, an unnecessary part of the leads is cut off and the leadterminals 2 b and 2 d are bent, thereby completing the semiconductordevice.

The metal block 47 is made of aluminum or copper, for example, and heatgenerated in the power chip 41 is emitted to the outside through thejointing material 46, the lead frame 2 a, the jointing material 48, themetal block 47 and an insulation layer 45 a (part of the mold resin 45).

The meal block 47 is entirely covered with the mold resin 45 to beinsulated from the outside. The jointing material 48 is not required toensure electric insulation between the lead frame 2 a and the metalblock 47. Thus, any material can be employed without considering itsinsulation breakdown voltage. Therefore, the jointing material 48 may bemade of a material such as solder that has a thermal conductivity betterthan that of the insulation layer 45 a. As a result, heat generated inthe power chip 41 is conducted well from the lead frame 2 a to the metalblock 47.

Further, the metal block 47 can be increased in size to the extent ofthe outside dimension of the mold resin 45 of the semiconductor devicewith the electrodes on the both surfaces of the power chip 41 insulatedfrom each other. As a result, improved heat radiation properties can beobtained.

More specifically, the metal block 47 has a surface opposite to thejointing material 48, which is larger than the other jointed to thejointing material 48. Accordingly, heat can be conducted with thejointing material 48 and the metal block 47 jointed to each other by aminimum area of almost the same size as the power chip 41, and anelectric circuit is formed by the lead frame 2 a at the peripheral partof the chip. Thus, size reduction is achieved, while heat generated inthe power chip 41 can be propagated from the jointing material 48 to themetal block 47 to the extent of the outside dimension of thesemiconductor device. As a result, it is possible to cause heat toconduct through the insulation layer 45 a by a larger area, and improvedheat radiation can be obtained.

Further, since the metal block 47 is jointed to the lead frame 2 a onits other main surface opposite to the power chip 41, it is possible todetermine size of the metal block 47 without affecting the wiring of thealuminum wire 44.

Furthermore, the lead frame 2 a and the metal block 47 are jointed justbefore the molding step such manufacturing can be performed up to thewiring of the aluminum wire 44 by the same process and apparatus asconventional ones. This permits a reduction of new capital investmentsand the like.

On the other hand, providing the metal block 47 on the other mainsurface of the lead frame 2 a results in an increase in a contact areawith the mold resin flow in the molding step and also in an increase inthe accompanying viscous force.

In the power semiconductor device according to the first embodiment,however, the lead frame 2 a with the power chip 41 mounted on its oneside main surface and the metal block 47 mounted on the other mainsurface has the plurality of suspension lead parts 2 b and 2 e. The leadframe 2 a is thus brought into a state of a beam supported at two ormore positions in the molding step for sealing the mold resin 45. Thiscan improve the stiffness of the lead frame 2 a.

As a result, the mold resin 45 can be maintained in a uniform thickness,and the insulation layer 45 a of the mold resin 45 under the metal block47 can be made thinner. Therefore, improved heat radiation propertiescan be obtained while securing insulation properties.

<Second Preferred Embodiment>

FIG. 10 is a plan view schematically illustrating a planar structure ofa power semiconductor device according to the second preferredembodiment of the invention before resin sealing. FIG. 11 is a sectionalview schematically illustrating a sectional structure of the powersemiconductor device according to the second embodiment after the resinsealing. FIG. 11 corresponds to a section along the line B—B of FIG. 10after the resin sealing.

Referring to FIGS. 10 and 11, a method of manufacturing the powersemiconductor device according to the second embodiment will bedescribed.

A plurality of power chips 41 and a plurality of integrated circuitchips 42 are mounted on one side main surfaces of the lead frames 2 aand 2 c, respectively, with the jointing material 46 using the diebonding technique. At this time, as shown in FIG. 11, a plurality ofseparated (partial) lead frames 2 ap each have the one side main surfaceon which at least one power chip 41 is mounted.

Thereafter, each of the power chips 41 is electrically connected to apredetermined inner lead of the lead frame 2 a and part of inner leadsof the inner lead frame 2 c by the aluminum wire 44 using the diebonding technique. The integrated circuit chip 42 and a predeterminedinner lead of the lead frame 2 c are also electrically connected by thegold wire 43.

Next, a plurality of partial metal blocks 47 p are mounted on the othermain surfaces of the plurality of partial lead frames 2 ap. Morespecifically, The plurality of partial metal blocks 47 p are placed onthe other main surfaces of the partial lead frames 2 ap and jointedthereto with the jointing material 48 so as to have one-to-onecorrespondence with a plurality of power chips 41 and to face acorresponding one of the power chips 41, respectively.

Thereafter, transfer molding is performed to seal the whole. A gapbetween adjacent partial metal blocks 47 p and 47 p is filled with themold resin 45, and the metal blocks 47 p are insulated from one another.Accordingly, the plurality of power chips 41 can be provided within asingle power semiconductor device while the partial metal blocks 47 premain insulated from one another.

The plurality of partial metal blocks 47 p are made of aluminum orcopper, for example, as in the first preferred embodiment. Heatgenerated in each of the power chips 41 is emitted to the outsidethrough the jointing material 46, the lead frame 2 a, the jointingmaterial 48, the metal block 47 and the insulation layer 45 a.

The jointing material 48 is not required to ensure electric insulationbetween the lead frame 2 a and the metal block 47 as in the firstembodiment. Thus, any material can be employed without considering itsinsulation breakdown voltage. Therefore, the jointing material 48 may bemade of a material such as solder that has a thermal conductivity betterthan that of the insulation layer 45 a. As a result, heat generated ineach of the power chips 41 is conducted well from the lead frame 2 a tothe metal block 47.

The power semiconductor device according to the second embodiment havingthe above-described structure further achieves the following effects inaddition to the same effects obtained in the first embodiment.

There is concern that by using the plurality of partial metal blocks 47p, an increase in the viscous force and the complexity of the flow maycause variations in the thickness of the resin under the lead frames 2ap on which the power chips 41 are mounted.

In the semiconductor device of the second embodiment, however, the(partial) lead frames 2 ap for the power chip each have the suspensionlead part 2 e provided thereon as in the first embodiment, and thus canbe supported by the plurality of suspension lead parts (2 b, 2 e) in themolding step.

As a result deformation (or displacement) of the lead frames 2 ap issuppressed such that the mold thickness under the metal blocks 47 p is auniform thickness. Thus, high heat radiation properties can be achievedwhile maintaining insulation properties.

FIG. 12 is an explanatory view schematically illustrating the state ofpartial metal blocks 47 p adjacent to each other. As shown in FIG. 12,the lead frames 2 ap on which the power chips 41 are mounted are longand thin extending diagonally with respect to an injecting direction ofthe mold resin. Thus, the lead frames 2 ap are deformed (or displaced)and bent in a direction perpendicular to the resin flowing directionsuch that there occurs a contact failure between adjacent lead frames 2ap and 2 ap.

However, since the structure in which the suspension lead part 2 e isprovided as described above permits a substantial suppression ofdeformation of the lead frames 2 ap in the molding step, adjacentpartial metal blocks 47 p and 47 p are reliably prevented from being incontact with each other by their lead frames 2 ap and the otherelements. This permits a reduction in the thickness of the mold resin 45between the adjacent partial metal blocks 47 p and 47 p. Thus, higherheat radiation properties can be achieved, and the power semiconductordevice can be reduced in size.

The plurality of partial metal blocks 47 p are placed in one-to-onecorrespondence with a plurality of power chips 41 and face acorresponding one of the power chips 41, respectively. Each of the metalblocks can thus be employed in correspondence with the power chips 41.In consequence the power chips 41 have a uniform temperature. This makesit easier to obtain operation assurance of the power semiconductordevice and permits an extension of the life of the power chips 41.

<Third Preferred Embodiment>

FIG. 13 is a plan view schematically illustrating a peripheral structureof a suspension lead part of a power semiconductor device according tothe third preferred embodiment of the invention. As shown in FIG. 13, anend of the suspension lead part 2 e is disposed in a cavity 56 formed inthe peripheral region of the mold resin 45. This structure allows thelength of the suspension lead part 2 e formed in the region 55 (FIGS. 6and 10) to be shorter than that in the case where the mold resin 45 doesnot have a cavity. Accordingly, it is possible to increase the stiffnessof the lead frame 2 a of the power chip 41 in the molding step. As aresult, the lead frame 2 a is hardly deformed, allowing the moldthickness to be made still thinner, and a power semiconductor devicewith less thermal resistance and excellent heat radiation properties canthus be obtained.

Further, providing the cavity 56 for the mold resin 45 permits anincrease in a creepage distance which is an insulation distance betweenthe suspension lead part 2 e projecting from the mold resin 45 and anouter periphery of the mold resin 45. Thus, improved insulationproperties can be obtained without increasing the size of thesemiconductor device.

<Fourth Preferred Embodiment>

FIG. 14 is a plan view schematically illustrating a peripheral structureof a suspension lead part of a power semiconductor device according tothe fourth preferred embodiment of the invention. As shown in FIG. 14,the end of the suspension lead part 2 e is disposed in the cavity 56formed on the mold resin 45 as in the third embodiment, and is cut insuch a manner as to be fit into the cavity 56.

More specifically, in the present embodiment, the end of the suspensionlead part 2 e is cut at an inner position with respect to the outermostsurface of the mold resin 45. As a result, the end of the suspensionlead part 2 e is fit into the cavity 56.

As described above, the power semiconductor device according to thepresent embodiment, in which the suspension lead part 2 e is fit intothe cavity 56 of the mold resin 45, achieves the effect of preventinginconvenience of being caught in at packaging and handling, therebysimplifying handling, in addition to the effects achieved by the thirdembodiment.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A semiconductor device comprising: first andsecond semiconductor chips; first and second lead frames having one sidemain surface on which said first and second semiconductor chips aremounted, respectively; a metal block provided on the other main surfaceof said first lead frame; and resin formed to cover said first andsecond semiconductor chips, said first and second lead frames and saidmetal block, wherein said first lead frame has a plurality of suspensionlead parts projecting from said resin, wherein said first semiconductorchip includes a plurality of first semiconductor chips, said first leadframe includes a plurality of first partial lead frames, said metalblock includes a plurality of partial metal blocks, and said pluralityof first partial lead frames each have one side main surface on which atleast one of said plurality of first semiconductor chips is mounted, theother main surface on which at least one of said plurality of partialmetal blocks is provided and a plurality of suspension lead partsprojecting from said resin.
 2. The semiconductor device according toclaim 1, wherein said metal block is provided to face said firstsemiconductor chip.
 3. The semiconductor device according to claim 1,wherein said metal block is jointed to the other main surface of saidfirst lead frame with a jointing material and has one surface oppositeto the other surface in contact with said jointing material, said onesurface being larger than the other surface.
 4. The semiconductor deviceaccording to claim 1, wherein said first semiconductor chip includes apower chip.
 5. The semiconductor device according to claim 4, whereinsaid second semiconductor chip includes an integrated circuit chip forcontrolling said first semiconductor chip.
 6. The semiconductor deviceaccording to claim 4, wherein said power chip includes at least one ofan insulated gate bipolar transistor and a fly wheel diode.
 7. Thesemiconductor device according to claim 1, wherein said plurality ofpartial metal blocks have one-to-one correspondence with said pluralityof first semiconductor chips and are provided to face a correspondingone of said first semiconductor chips, respectively.
 8. A semiconductordevice comprising: first and second semiconductor chips; first andsecond lead frames having one side main surface on which said first andsecond semiconductor chips are mounted, respectively, a metal blockprovided on the other main surface of said first lead frame; and resinformed to cover said first and second semiconductor chips, said firstand second lead frames and said metal block, wherein said first leadframe has a plurality of suspension lead parts projecting from saidresin, wherein said resin has a cavity in a peripheral region thereof,and at least one of said plurality of suspension lead parts is disposedin said cavity.
 9. The semiconductor device according to claim 8,wherein at least one of said plurality of suspension lead parts isprovided to fit into said cavity.
 10. The semiconductor device accordingto claim 8, wherein said metal block is provided to face said firstsemiconductor chip.
 11. The semiconductor device according to claim 8,wherein said metal block is jointed to the other main surface of saidfirst lead frame with a jointing material and has one surface oppositeto the other surface in contact with said jointing material, said onesurface being larger than the other surface.
 12. The semiconductordevice according to claim 8, wherein said first semiconductor chipincludes a power chip.
 13. The semiconductor device according to claim12, wherein said second semiconductor chip includes an integratedcircuit chip for controlling said first semiconductor chip.
 14. Thesemiconductor device according to claim 12, wherein said power chipincludes at least one of an insulated gate bipolar transistor and a flywheel diode.